1. Field of the Invention
The present invention relates to a security surveillance system.
2. Description of the Related Art
Generally, security surveillance cameras for monitoring persons who enter into or exit from banks and large buildings are located at various places. The security surveillance cameras are connected to the management host of a guard room or a central control room, thus dealing with abnormal situations.
FIG. 1 is a diagram showing the schematic construction of a conventional security surveillance system, and FIG. 2 is a diagram showing the schematic construction of a security surveillance camera used in the system of FIG. 1.
Referring to FIGS. 1 and 2, the conventional security surveillance system includes one or more security surveillance cameras 111 to 114 for compressing (Moving Picture Experts Group (MPEG) encoding) a captured moving image and transmitting the compressed image to a management host 200, and the management host 200 for reproducing and displaying compressed moving images respectively transmitted from the security surveillance cameras 111 to 114. Each of the security surveillance cameras 111 to 114 has a moving image compression unit 121, 122, 123 or 124 which is described in detail below with reference to FIG. 2.
Each of the security surveillance cameras 111 to 114 converts an optical signal, entering through a lens 11, into an electrical signal using an image sensor 12. Thereafter, the electrical signal is converted into a digital signal, and the digital signal is converted into a moving image signal having a predetermined format determined by a digital signal processor 13. Thereafter, the digital moving image signal is encoded and compressed by a moving image compression unit 14, and is transmitted to the management host 200 through an interface 15. Eventually, the management host 200 receives compressed moving images from the security surveillance cameras 111 to 114, respectively, decodes them through decoders 211 to 214 and then displays the decoded moving images on displays 241 to 244. The security surveillance cameras 111 to 114 and the management host 200 are controlled by a control unit 230. If necessary, the moving image data may be stored in memory 220.
A camera unit 100 having the security surveillance cameras 111 to 114 is physically separated from the host 200, so that the moving images are transmitted between the cameras 111 to 114 and the host 200. In the case where the camera unit 100 and the host 200 are connected to each other via the Internet or in some other digital manner, or the management host 200 controls a number of cameras 111 to 114, the management host 200 is connected to a number of cameras 111 to 114, retrieves image data from the cameras 111 to 114, and displays the retrieved image data on the screen or stores them in another recoding medium.
Since it is impossible to simultaneously receive the image data output from many cameras, and store or display them, the cameras compress and transmit the moving images. Such compression decreases the amount of data output from the cameras, so that it facilitates the display of the data on the screen and the storage of the data in another recoding medium.
However, when a moving image is highly compressed, an original screen is distorted or obscured, so that a user cannot clearly view the content of the screen. Accordingly, when using the conventional security surveillance cameras, user can view or determine current situations when the situations occur, but stored images or displayed images are not clear enough to distinguish profiles, thus degrading the security surveillance function.